Flattening a puckered cyclohexasilane ring by suppression of the pseudo-Jahn-Teller effect

We report the experimental and theoretical characterization of neutral Si6X12 (X = Cl, Br) molecules that contain D-3d distorted six-member silicon rings due to a pseudo-Jahn-Teller (PJT) effect. Calculations show that filling the intervenient molecular orbitals with electron pairs of adduct suppresses the PJT effect in Si6X12, with the Si-6 ring becoming planar (D-6h) upon complex formation. The stabilizing role of electrostatic and covalent interactions between positively charged silicon atoms and chlorine atoms of the subject [Si6Cl14](2-) dianionic complexes is discussed. The reaction of Si6Cl12 with a Lewis base (e.g., Cl-) to give planar [Si6Cl14](2-) dianionic complexes presents an experimental proof that suppression of the PJT effect is an effective strategy in restoring high Si-6 ring symmetry. Additionally, the proposed pathway for the PJT suppression has been proved by the synthesis and characterization of novel compounds containing planar Si-6 ring, namely, [(BuN)-Bu-n-N-4] 2[Si6Cl12I2], [(Bu4N)-Bu-n](2)[Si6Br14], and [(Bu4N)-Bu-n](2)[Si6Br12I2]. This work represents the first demonstration that PJT effect suppression is useful in the rational design of materials with novel properties. (c) 2011 American Institute of Physics. [doi:10.1063/1.3516179]